How Does Oxygen Transform into Nitrogen in ITER's Fusion Reactor?

[cmb]

I don't understand this line in iter website. How is this reaction possible?

"When exposed to the intense flux of neutrons from the fusion reaction, the oxygen present in the water generates short-lived radioactive isotopes of nitrogen—one (isotope 16) emitting a highly energetic gamma ray, the other (isotope 17) a fast neutron."

Is the neutron knocking out an oxygen proton, then? Is that very common, or the issue is the large neutron flux?

https://www.iter.org/newsline/-/3050

I also don't understand the decay mode; here is 16N in the wiki list of nitrogen isotopes;-

16N 7 9 16.0061017(28) 7.13(2) s
β− (99.99%) 16O
β−, α (.001%) 12C

I guess displacing the oxygen proton leaves the nucleus very excited?

I'd be grateful for any insight.

 

[Lord Jestocost]

When water is exposed to a neutron flux, a process termed "neutron activation" occurs: https://en.wikipedia.org/wiki/Neutron_activation

 

[cmb]

When water is exposed to a neutron flux, a process termed "neutron activation" occurs: https://en.wikipedia.org/wiki/Neutron_activation

I would have though neutron activation was...

16O + n = 17O?

OK, I can see on that page there is an immediate release of a proton. Does this make an intermediate 17O, then, or is the proton just knocked straight out?

 

[mfb]

16O + n = 17O?

¹⁷O is stable. You get some of that, too, but that doesn't matter. The (n,p) reaction where the neutron kicks out a proton is more important because it leads to further reactions.

I also don't understand the decay mode; here is 16N in the wiki list of nitrogen isotopes;-

16N 7 9 16.0061017(28) 7.13(2) s
β− (99.99%) 16O
β−, α (.001%) 12C

Most of the time it does a beta decay to oxygen, sometimes it emits an alpha particle at the same time.

 

[cmb]

Years ago I used to use a website where you could put in these sorts of reactions and it'd give you cross sections and things, I could have looked it up. But not sure where that is. Would you know a site/database I might be thinking of?

 

[Astronuc]

Years ago I used to use a website where you could put in these sorts of reactions and it'd give you cross sections and things, I could have looked it up. But not sure where that is. Would you know a site/database I might be thinking of?

Various countries and the EU have nuclear data centers. In the US, the database is maintained at Brookhaven National Laboratory (BNL)

www.nndc.bnl.gov
For cross sections of elements/nuclides, see https://www.nndc.bnl.gov/sigma/
For some information on radionuclides, see https://www.nndc.bnl.gov/nudat2/
N-16 was a concern for some BWR using hydrogen injection in the feedwater. In a reducing environment, nitrogen is carried out of the core by the steam through the steam lines to the turbines. Some plants had to add additional shielding, or restrict areas near the steam lines to prevent worker exposure.
https://www.nndc.bnl.gov/nudat2/decaysearchdirect.jsp?nuc=16N&unc=nds

The (n,p) reaction in ¹⁶O has a neutron energy threshold of ~10.2 MeV, so the concern is primarily about the 14.1 MeV neutron from the d+t fusion reaction, which is the principal reaction planned for ITER.

 

[Vanadium 50]

The (n,p) reaction where the neutron kicks out a proton is more important because it leads to further reactions.

@cmb, you might think about Newton's Cradle when thinking about these reactions. Because n and p have about the same mass, an n comes in and a p goes out. (This is modified by a bunch of nuclear physics, but it's a good starting point to visualize what happens)

 

[cmb]

Various countries and the EU have nuclear data centers. In the US, the database is maintained at Brookhaven National Laboratory (BNL)

www.nndc.bnl.gov
For cross sections of elements/nuclides, see https://www.nndc.bnl.gov/sigma/
For some information on radionuclides, see https://www.nndc.bnl.gov/nudat2/
N-16 was a concern for some BWR using hydrogen injection in the feedwater. In a reducing environment, nitrogen is carried out of the core by the steam through the steam lines to the turbines. Some plants had to add additional shielding, or restrict areas near the steam lines to prevent worker exposure.
https://www.nndc.bnl.gov/nudat2/decaysearchdirect.jsp?nuc=16N&unc=nds

The (n,p) reaction in ¹⁶O has a neutron energy threshold of ~10.2 MeV, so the concern is primarily about the 14.1 MeV neutron from the d+t fusion reaction, which is the principal reaction planned for ITER.

Thanks, that is super. Yes, EXFOR was the one I was thinking of.

@cmb, you might think about Newton's Cradle when thinking about these reactions. Because n and p have about the same mass, an n comes in and a p goes out. (This is modified by a bunch of nuclear physics, but it's a good starting point to visualize what happens)

I was thinking that, but does it happen most of the time in neutron capture, though, displacing p for n?

 

[Vanadium 50]

Given the number of nuclei and the large range of energies involved, "most of the time" is not well-defined.

 

[Astronuc]

neutron capture

'Neutron capture' by convention means that the neutron is absorbed and the nucleus of A increases in mass to A+1, e.g., ¹⁶O + n -> ¹⁷O (transmutation), and usually a gamma ray is emitted, a process called 'radiative capture'. The thresholds for (n,n'), (n,p), (n,α), or other reactions are usually in the MeV-range, typical of binding energies (of nucleons) of the target nucleus. We also observe photoneutron reactions for high-energy gammas, e.g., d+γ(~2.23 MeV) -> p+n, or ⁹Be+γ(~1.67 MeV) -> 2α + n, which is used in secondary neutron sources in nuclear reactors. The gamma source is ¹²³Sb, which absorbs a neutron and becomes ¹²⁴Sb, which then decays and emits a gamma of ~1.69 MeV.

https://journals.aps.org/pr/abstract/10.1103/PhysRev.80.309

https://inis.iaea.org/collection/NCLCollectionStore/_Public/14/792/14792880.pdf (~1982)
http://nuclear.ee.duth.gr/upload/2009 NIMS SbBe.pdf

When a high energy particle (e.g., neutron, proton, . . . ) interacts with a nucleus and knocks out particles, we refer to 'spallation', or sometimes 'fission'.
https://inis.iaea.org/collection/NCLCollectionStore/_Public/23/015/23015552.pdf

Also, in a nuclear reactor, besides the fission reactions and decays of fission products, absorption of neutrons leads to transmutation of structural materials, about which we have to be concerned.